The present invention relates to degradation of pollutants using anaerobic methods. Alkanes, e.g., methane, ethane, propane and butane, are used to effectively degrade pollutants such as tetrachloroethylene. The alkanes may accelerate anaerobic respiration.
Tetrachloroethylene (PCE) and carbon tetrachloride (CT) are two metal degreasing and dry cleaning solvents which are recalcitrant pollutants detected in the soil and groundwater at many contaminated sites. Under aerobic conditions, PCE and CT have traditionally been considered nonbiodegradable. Under anaerobic conditions, PCE and CT may be reductively dechlorinated by mixed microbial populations to less-chlorinated ethenes.
PCE is currently remediated using chemicals that enhance anaerobic degradation within the subsurface. Carbon sources such as acetate and methanol are injected into the subsurface where oxygen is limited or absent and alternate electron acceptors such as nitrate or sulfate are available. Chemicals that slowly release hydrogen in groundwater are also used to accelerate anaerobic degradation processes.
PCE may not be very susceptible to aerobic metabolic pathways. Research conducted under aerobic conditions using pure cultures and limited consortia of butane-utilizing bacteria has indicated that butane oxidation may not degrade or cometabolize PCE even though butane enrichment results in the expression of a wide variety of oxygenases during butane oxidation (Hamamura N., R. Storfa, L. Semprini, and D. J. Arp. xe2x80x9cDiversity in Butane Monooxygenases among Butane-Grown Bacteria. Appl. Environ. Microbiol. 65(10):4586-4593, 1999).
The bioremediation of various pollutants using butane-utilizing bacteria is disclosed in U.S. Pat. Nos. 5,888,396, 6,051,130, 6,110,372 and 6,156,203, and U.S. application Ser. No. 09/275,320, which are incorporated herein by reference. The disclosed methods primarily focus on the cometabolism of pollutants using butane-utilizing bacteria under aerobic conditions.
In accordance with the present invention, alkanes are used to degrade pollutants such as recalcitrant chlorinated compounds under anaerobic conditions, e.g., through reductive processes such as dechlorination. In a preferred embodiment, butane is used as a low molecular weight organic compound which serves as an electron donor under anaerobic conditions.
An aspect of the present invention is to provide a method of degrading a pollutant. The method includes treating the pollutant by supplying an alkane in the substantial absence of oxygen to stimulate the growth of anaerobic bacteria which degrade the pollutant.
Another aspect of the present invention is to provide an anaerobic bioremediation system. The system includes means for supplying an alkane to a contaminated site in the substantial absence of oxygen to stimulate the growth of anaerobic bacteria which degrade a pollutant at the contaminated site.
A further aspect of the present invention is to provide an in-situ anaerobic bioremediation system which includes a source of an alkane, and at least one injector in flow communication with the source of the alkane.
These and other aspects of the present invention will be more apparent from the following description.